Add tests that invoke a linker which uses generated linker scripts from slinky

[AngheloAlf]

Have dummy projects (with dummy C and asm files) that get built and linked using linker scripts generated by slinky.

Would be nice a few multiple projects that aim to represent multiple kinds of projects/platforms/variants, so we don't miss anything. Including but not limited to:

• N64
  • IDO
  • KMC
  • EGCS
  • Out of normal RAM segments
  • Multiple overlays
  • Shared vram overlays
• PSX
  • PSX-EXE
  • Overlays (or whatever they are called)
  • No use of $gp register (-G0)
  • Hardcode the $gp register in the yaml
  • Shiftable $gp register
• PS2
  • idk
• GC / Wii
  • idk

Make sure the produced binary and mapfile is still the same as expected